Disabled persons who are confined to wheelchairs have often found their mobility and, hence, their activities limited by the capabilities of the wheelchairs available to them. The efforts of architects and planners to make public places and private spaces accessible to the wheelchair-bound can be thwarted by the limitations of the very wheelchairs on which the handicapped must depend for access to all parts of their environment. Currently, available wheelchairs include those that are motor driven and those that are driven manually. The high cost of motor driven wheelchairs, which are powerful enough to negotiate many different types of surfaces and terrains, puts them beyond the reach of large numbers of those who need them. The available manually driven wheelchairs, moreover, are often difficult to drive, especially up inclines, over curbs and on uneven terrain. In addition, the majority of these wheelchairs restrict the user to a sitting position. Those wheelchairs that enable their users to assume a standing position are expensive, complex and uncomfortable.
The design of currently available manually driven wheelchairs, moreover, presents many disadvantages and limitations. Two large drive wheels, which are usually positioned on each side near the center of gravity of the wheelchair, support the wheelchair and contact the ground, floor or other base surface on which the wheelchair rests. These large wheels are moved by the user's hands to propel the wheelchair in the direction desired. Smaller, pivoting front wheels allow the user to control the direction of travel of the wheelchair by varying the energy directed to the right or left large drive wheel. This system may work reasonably well on smooth flat surfaces. However, the small pivoting front wheels do not maneuver the wheelchair well up curbs or over large bumps, requiring the user to obtain assistance to travel over these obstacles. In addition, as the forward speed of the wheelchair increases, the pivoting front wheels make steering more difficult. Finally, because the user must usually contact the large drive wheel directly to propel the wheelchair, the user's hands and clothing are easily dirtied during travel, particularly during inclement weather and during travel over dirty or undesirable surfaces.
The available options for improving the suspension and, thus, the smoothness of travel of manually operated wheelchairs are limited. Moreover, maximum user control of travel is often sacrificed in favor of improving the suspension. As a result, the user may be required to choose between a smooth riding wheelchair and a wheelchair that he or she can control more easily.
The gearing and braking of a direct drive manual wheelchair is cumbersome and complicated by the chair's design. Unfortunately, because of this, the user's range of travel without assistance may be severely limited. For example, a ramp with an incline of more than 5 to 7 degrees will require the wheelchair user to obtain assistance to negotiate this incline successfully. In addition, obstacles like curbs are virtually impossible to negotiate with the existing gearing and braking systems used on most manually driven wheelchairs without assistance. This need for assistance, moreover, limits the wheelchair user's independence.
The prior art includes a large number of different types of manually driven wheelchairs. Those described in U.S. Pat. Nos. 4,231,614 to Shaffer; 4,380,343 to Lovell et al.; 4,614,246 to Masse et al.; and 4,625,984 to Kitrell are illustrative of these many prior art designs. The patents to Lovell et al. and Kitrell disclose wheelchairs driven by hand wheals which are manually rotated by the user to drive separate drive wheels to propel the chair. Although these arrangements allow the wheelchair occupant to avoid dirtying his or her hands or clothing since the hand wheel does not directly contact the ground or other travel surface, the chain drives and belt drives used to drive these chairs do not overcome the travel limitations posed by manually driven wheelchairs. The occupant is not able to negotiate inclines or obstacles more easily or without assistance with the wheelchairs disclosed in these patents.
The wheelchairs disclosed by Masse et al. and Shaffer have stationary front wheels and pivoted back wheels. While this design provides some improvements in maneuverability, the wheelchair user still must rely on assistance from others for complete mobility with the wheelchairs described in these patents. The aforementioned prior art, therefore, does not provide a manually driven wheelchair which allows the user substantially complete mobility without assistance.
To allow the wheelchair user virtually unlimited mobility, the chair should support the user adequately in a sitting position for travel. The chair should, in addition, permit the user to assume a standing position supported as needed by the wheelchair in a manner that permits the user to use and, thus, strengthen those parts of the body which he or she is capable of using. Wheelchairs that adjust to support the occupant in both a sitting and a standing position are known. For example, the wheelchair disclosed in U.S. Pat. No. 4,809,804 to Houston et al. achieves this objective. However, the seat assembly in this patent is a complex, motor driven apparatus that leaves the occupant in an extremely uncomfortable upright position in which he has only limited mobility. Moreover, the center of gravity changes as the chair moves from a sitting to a standing position so that the wheelchair is not as stable as it should be to support a disabled person in an unaccustomed position. The prior art, therefore, does not disclose a manually operated wheelchair which can be easily adjusted manually to support the occupant in either a sitting or a standing position so that the occupant has maximum mobility in both positions.
Consequently, a need exists for a simple, manually driven wheelchair which does not limit the mobility of the occupant, but which permits the occupant to negotiate unassisted almost any type of terrain or travel surface likely to be encountered. A need also exists for a manually driven wheelchair which can be easily adjusted by the user to support the user in either a sitting or a standing position so that the center of gravity does not change during the shift from a sitting to a standing position, but remains the same to provide maximum stability to the chair and, hence, the occupant.